ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-7-677-2007Non-volatile residuals of newly formed atmospheric particles in the boreal forestEhnM.1PetäjäT.1BirmiliW.12JunninenH.1AaltoP.1KulmalaM.11Division of Atmospheric Sciences, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland2Leibniz-Institute for Tropospheric Research, Permoserstrasse 15, 04318, Leipzig, Germany1202200773677684This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/7/677/2007/acp-7-677-2007.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/677/2007/acp-7-677-2007.pdf

The volatility of sub-micrometer atmospheric aerosol particles was
studied in a rural background environment in Finland using a
combination of a heating tube and a scanning mobility particle
sizer. The analysis focused on nanoparticles formed through
nucleation which were subsequently observed during their growth in
the diameter range between 5 and 60 nm. During the 6 days of new
particle formation shown in detail, the concentrations of newly
formed particles increased up to 10 000 cm<sup>&minus;3</sup>. The number of
nucleation mode particles measured after volatilization in the
heating tube at 280&deg;C was up to 90% of the total number
under ambient conditions. Taking into account the absolute
accuracy of the size distribution measurements, all ambient
particles found in the rural atmosphere could have a non-volatile
core after volatilization at 280&deg;C. As the regional new
particle formation events developed over time as a result of
further vapor condensation, the newly formed particles grew at an
average growth rate of 2.4&plusmn;0.3 nm h<sup>&minus;1</sup>. Importantly, the
non-volatile cores of nucleation mode particles were also observed
to grow over time, however, at a lower average growth rate of 0.6&plusmn;0.3 nm h<sup>&minus;1</sup>. One implication of the volatility analysis
is that the newly formed particles, which have reached ambient
diameters of 15 nm, are unlikely to consist of sulfuric acid,
ammonium sulfate, and water alone. A relatively constant ratio
between the growth rate of the ambient particles as well as their
non-volatile cores indicates that non-volatile matter is formed
only gradually in the growing particles. The non-volatile fraction
of the particles showed some correlation with the ambient
temperature. The composition and formation mechanism of this
non-volatile material in nucleation mode particles are, to date,
not known.